Pseudomonas aeruginosa bacteria use physical collisions with neighbours as information, dynamically switching between disorder and coordinated movement without chemical signalling.
When crowded cells collide, mechanosensitive type IV pili trigger rapid reversals that prevent the population becoming trapped in an overly ordered state. At a colony’s less-crowded edge, reversals diminish and cells instead align into packs moving toward open territory. In micro-mazes, wild-type bacteria explored about 92% of the maze and 20% reached the exit, while only 1% of non-reversing mutants escaped within four hours.
https://phys.org/news/2026-10-bacteria-collisions-crowded-environments-micro.html
